Recently, with diversification of consumer's dietary habits, a wide variety of drinks have been required and thus a variety of commercial product groups have been developed. Among them, milk-type foods and drinks (foods and drinks such as milk, processed milk, milk drinks, lactic acid bacteria drinks, milk-blended drinks; hereinafter also referred to as “cow's milk etc. for drinking and milk products”) have been considered to be promising also in the future as health-promoting drinks from the viewpoint of various nutrients intrinsically possessed by cow's milk etc.
In general, because of no exposure to light for a long time in distribution routes, cow's milk for door-to-door delivery can be provided after it is packed in a transparent bottle, but the cowls milk etc. for drinking and milk products displayed and sold at the store are usually provided after they are packed in light-shielding paper containers or plastic containers. In such cow's milk etc. for drinking and milk products, milk components such as milk fat contained therein have undergone oxidation through the exposure to light such as sunlight and fluorescent light when they are displayed at the store, and thereby, abnormal smell referred to as off-flavor is sometimes generated, which is different from the original smell. In order to prevent the generation of the off-flavor, the cow's milk etc. for drinking and milk products are packed in containers possessing a light-shielding property and then displayed and sold.
The off-flavor generated from cow's milk etc. for drinking and milk products is mainly attributable to photooxidation of milk components such as milk fat. Main components of the off-flavor are certain kinds of aldehydes and the like and they are not problematic with regard to quality of the product. However, the flavor is much different from the original one and thus the commercial value thereof is remarkably lowered.
On the other hand, recently, as one of various measures for enhancing the consumption of cow's milk etc. for drinking and milk products, a variety of containers have been investigated. Among them, polyethylene terephthalate containers, so-called PET bottles are frequently used as one factor for leading the drink market because of their recycling efficiency, re-capping ability, high barrier property, and the like. In particular, since the content can be visually checked, consumers can also obtain the sense of relief. Therefore, use of these transparent PET bottles for the cow's milk etc. for drinking and milk products is considered to be promising but the aforementioned problem of off-flavor should be solved as an essential problem.
As solutions thereof, various measures have been investigated. For example, for packaging products such as cow's milk, quality deterioration of the products is prevented by molding a container with adding or laminating a specific pigment composition to enhance a light-shielding property (see, Patent Documents 1, 2, and 3, and the like).
As other solutions, there have been proposed a method of adding a certain additive to milk products and a method of solving the problem by performing a certain treatment on milk products. For example, there may be mentioned a method of decreasing the formation of unpleasant smell in milk products due to photooxidation by adding ascorbic acid to milk products such as cow's milk (Patent Document 4), a method of preventing the generation of off-flavor by adding vitamin E to milk-mixed specialized drinks (Patent Document 5), a method of preventing the generation of off-flavor due to photoinduction by subjecting milk drinks/foods to a heat treatment under specific conditions (Patent Document 6), and the like methods.
However, with regard to the light-shielding container adopted in the above conventional art, the content substantially cannot be visually checked from the outside, unlike so-called transparent containers. Therefore, the above container deviates from the primary object, to be a transparent container, and hence cannot be employed. Moreover, the conventional technology in which an additional additive is used cannot be applied since it is forbidden to use any additive in cow's milk for drinking. Furthermore, in the case that an additive is applied to cow's milk etc. for drinking and milk products, the flavor thereof may be impaired and also the production process and product costs are influenced.
Patent Document 1: JP-A-8-283495
Patent Document 2: JP-A-2005-523845
Patent Document 3: JP-A-2005-178850
Patent Document 4: JP-A-10-844866
Patent Document 5: JP-A-2000-228952
Patent Document 6: JP-A-2002-262769